1. Field of the Invention
The present invention is directed to a high efficiency impeller-type aerator for oxygenating the water supply of aquatic organisms, such as fish in a fish tank or bait in a live well.
2. Description of the Related Art
When fishing from a boat, it is a common practice to bring along bait fish in closed tanks known as live wells. Alternatively, larger boats may be equipped with a thru-hull bait well, wherein water from outside the boat is continuously pumped in, is passed through the tank, and is discharged over the side. In order to keep the bait fish alive for long periods of time, an aerator is provided to replenish the oxygen in the water as it is depleted by the bait fish. Several distinct types of aerators have been developed.
For example, U.S. Pat. No. 3,822,498 teaches an aerator for a live well wherein water is sucked through a pump and sprayed out a distributor manifold in the form of small jets above the surface of the water. As the jets pass through the air and then strike the surface of the water, the water picks up dissolved oxygen and entrained air bubbles. These systems are, however, disadvantageous for a number of reasons.
First, it is inevitable that jets of water will strike the fish and wash away the mucus outer coating which protects the fish. Second, energy consumption is high. Third, while the surface area of the live well may be aerated, the lower reaches of the bait well are not aerated, particularly when a large number of bait fish are kept in the bait well. Finally, aeration efficiency is relatively low, so that the total number of bait fish which can be kept in the well is correspondingly limited.
The aerator described in U.S. Pat. No. 5,582,777 (Vento et al), which utilizes a centrifugal pump, achieves a significantly improved level of oxygenation of the water in a live well while producing a gentle action which does not harm the bait fish. In fact, the unusually high level of oxygenation makes it possible to pack two to four times as many bait fish into a live well as had previously been possible.
The Vento et al use of the impeller cavity of a centrifugal or impeller type pump as an aerator mechanism represented a departure from conventional thinking, since it is the common experience of those in the industry that as air is introduced into the centrifugal pump it accumulates around the impeller, resulting in air-lock. That is, the accumulated air causes the impeller to spin freely, without pumping water. When water is not pumped through a live well, bait fish begin dying. Thus, conventional thinking was to take measures to prevent any air from getting into the centrifugal pump. Vento et al discovered that by regulating the amount of air introduced to the upstream (suction) side leading to a centrifugal pump, it becomes possible to induce a very thorough mincing of air and water in the pump impeller, resulting in emission of very fine mist of bubbles from the downstream (emission) side of the pump, without the problem of loss of suction. In other words, by supplying just the right proportions of air and water into the pump impeller, significant aeration can occur without the above-described problem of air lock.
Although the level of aeration is significantly improved with the Vento et al aerator as compared to conventional pumps using the same amperage, the inventor has noticed that there are two problems associated with this system. The first is that the Vento et al arrangement requires regulation of the input of air, either manually (via valve, clamp, etc.) or automatically (via optical turbidity sensors, etc.). The second is that the output from a centrifugal pump, once modified to introduce air according to the Vento patent, drops dramatically, for example, from 500 gallons per hour to 200 gallons per hour, thus the pump is operating at only 40% of its intended capacity.
In view of the foregoing, it is an object of the present invention to provide an improved centrifugal type aerator which does not require monitoring or regulating of the air input.
It is a further object of the present invention to provide an aerator which exhibits an improved capacity or flow rate.
It is a further object of the present invention to provide an aerator designed to avoid vapor lock of the centrifugal pump impeller.
It is yet a further object of the present invention to provide an aerator which achieves a high level of oxygenation.